M. Cantera > wrote:
>On Thu, 06 Oct 2005 00:33:31 GMT,
>(Leon van Dommelen) wrote:
>
>>M. Cantera > wrote:
>>
>>>On Sun, 02 Oct 2005 11:55:32 GMT,
>>>(Leon van Dommelen) wrote:
>>>
>>>>M. Cantera > wrote:
>>>>
>>>>>On Sat, 01 Oct 2005 16:38:28 GMT, "tooloud" >
>>>>>wrote:
>>>>>
>>>>>>The other day, I had to laugh as I watched a guy stop a C6 Corvette in a
>>>>>>SuperTarget parking lot, open the hood, check the oil, and pour an entire
>>>>>>quart into the engine. He didn't seem surprised to be doing this.
>>>>>>
>>>>>>I wanted to run over and scream "But it's a brand new car!"
>>>>>
>>>>>It is normal for new engines to consume oil during the break in period
>>>>>(it is called that because the moving surfaces such as piston rings
>>>>>need to wear down rough spots. Oil leaks past the rough spots during
>>>>>breaking-in).
>>>>
>>>>There should not be rough spots with modern tolerances.
>
>>>
>>>Cast iron cylinder bores aren normally honed is cross hatched pattern
>>>at about 45 degrees to the piston travel they need not be as smooth as
>>>possible (relatively speaking) . This is to allow the new rings, which
>>>are tapered on the outside and which are compressed by the cylinder
>>>wall, to wear themselves into the shape against the cylinder. The wear
>>>process normally takes place within the first 50 hours of operation
>>>after which oil comsumption stabilizes.
>>>
>>>This is why manufacturer advise against operating a new engine at
>>>constant rpm and loads for extended periods of time.
>>
>>They used to when tolerances were not what they are now, and
>>have been for many years. For example, Mazda already stated for the
>>1989 Miata that no special break-in is necessary. And I did not use
>>a drop of oil during the break in, let alone the quart you appear
>>to find normal.
>
>I did not state that a one quart was normal for a 1.8 liter Mazda
>engine.
>
>Also, all engines consume oil during normal operation. An engine with
>abnormally low oil use is not lubricating the compression rings.
>Metal to metal contact is not good. If you can not detect oil
>comsumption in an engine, it is either because the oil change interval
>is too short or the accumulation of contaminats in the oil is equal to
>the rate of oil use.
>
>The Mazda 1.8 has 83 mm bore and 85 mm stroke. The original post
>referred to a Corvette which is equiped with a 5.5 liter engine with
>99 mm bores and a 92 mm stroke. The cylinder area swept by the top
>compression ring is 88600 and 228900 square millimeters respectively.
>One engine has 2.57 times greater cylinder surface area than the
>other. Opertating conditions being the same, I would expect oil
>comsumption rates to be proportionally less in the smaller engine when
>operated at similar rpms and loads. Assuming a full quart was
>required of the Corvette engine would be 0.4 quarts in the Miata.
Your point about the larger swept cylinder surface area in the Corvette
engine is well taken. It would be hard for us Miata owners to note less
than half a quart of oil loss, so maybe the Corvette observation is not
as far out as it seemed.
>>
>>Mazda does recommend that you do not maintain a constant speed for
>>long during the first 600 miles, since it *may* add to performance,
>>economy, and life of your Mazda. However, Mazda does not advise against
>>doing those things.
>Lower performance perhaps because the engine does not achieve optimum
>compression due to impreperly seated rings?
Note the "perhaps" and "may" (on Mazda's part.).
>>Also, I am sure the only reason is a good polishing process of the
>>metal surfaces such as piston rings versus cylinders that you mention,
>>but not to stop oil leaks, as is apparently necessary for the Corvette.
>
>The polishing processdis to create the ideal surface that allows the
>right ammount of engine oil to adhere to the surface of the cylinder
>when the piston is at the top of the travel. The oil rings scrape the
>excess off leaving the oil in between the scratches. That oil is left
>to lubircate the rings on the compression and power strokes.
>
>The cylindel wall look like this when new: /\/\/\/\/\/\ with excess
>oil in the valleys exposed to the combustion chanber.
>
>After break in the it is more lime \_/\_/\_/\_/ (piston ring travels
>on the side of the flat spots.
>
>>Now the way I understand it, US manufacturers have been achieving
>>tolerances approaching those of the Japanese for quite some time now,
>>so it seems strange that the Corvette apparently does not in the 21st
>>century.
>>
>Acceptable oil use was 1 qt / 1000 miles for 1960 era v-8.
>>> Manufaturers
>>>also advise against operating at high rpms during break in because it
>>>can lead to oil "glazing" the cylinder walls and uneven break in of
>>>the rings.
>>
>>Mazda does not, and I would assume it to be the same for other foreign
>>manufacturers as well as US manufacturers meeting modern tolerances.
>>Anyone knows whether Honda puts a break-in restriction on the 9000
>>rpm of the S2000?
>
>
>See http://www.automotiverebuilder.com/ar/ar129832.htm for a good
>illustration of the modern piston and ring technology. Anyone
>familiar with the Toyota and VW sludging problems knows that some of
>the side effects or tighter tolerances are not always good.
I assume you mean "tight clearances", *not* "tight tolerances"?
Leon
>>
>>Leon
>>
>>>>
>>>>> The 6 liter C-6 engine has a 5.5 quart capacity so that
>>>>
>>>>The 1.8l Miata engine has 4 quarts, which is almost the same.
>>>
>>>>
>>>>>quart was not a hughe percentage of the engine capacity.
>>>>
>>>>Leon
--
Leon van Dommelen
Bozo, the White 96 Sebring Miata .)
http://www.dommelen.net/miata
EXIT THE INTERSTATES (Jamie Jensen)